For some six centuries before Ptolemy, philosophers and scientists had been debating the supposedly competing credentials of reasoning and of perceptual observation as guides in the quest for truth. Controversy continued into his time and beyond, and was as brisk among harmonic scientists as anywhere else. Earlier commentators had occasionally surveyed the battlefield; but there is little evidence that exponents of the science themselves, after the pioneering years of the fourth century bc, had developed their positions in the light of sober consideration of the merits and deficiencies of the warring camps. They seem, on the whole, simply to have taken up entrenched positions on one side or the other of longstanding barricades, and to have dismissed alternative positions out of hand.

Ptolemy is an important exception. He shows himself to be well informed about the debate, and he offers sharp criticisms of extreme views on either side. His own position is designed to incorporate promising insights from any doctrinal repertoire, while avoiding the faults they had previously carried with them, and to fuse them into a new methodological amalgam, more balanced and more adequate to its task. The business of the present chapter is to examine the statements he makes on these issues in the opening pages of the Harmonics. Here he is not reviewing the postures of his predecessors, though as we shall see immediately, they are implicitly under fire right from the start.